Make sure your heating the fitting not the pipe.
Make sure both fitting and pipe are brushed clean.
If you get the pipe and fitting at the same heat you will have problems.
You can wipe off any excess drip before it cools.
1. I just had it clamped to a 2x4 that was laying off the edge of a table. I just bought a black and decker workmate (wooden vice type thing). Am I better off wrapping the pipe in a towel or something where the vice squeezes it to insulate it?
No, it should be fine as long as the joint your soldering isn't clamped directly in the vise. If the joint is at the end of a few inches of pipe, you should be fine.